The present invention relates to packages for semiconductor devices, and in particular to using an adhesive material containing microcapsules to attach semiconductor components in a board-on-chip (BOC) package.
Semiconductor devices, for example dynamic random access memory (DRAM) devices, are shrinking in the sense that smaller devices are being manufactured that are able to handle larger volumes of data at faster data transfer rates. As a result, semiconductor manufacturers are moving toward chip-scale packages (CSP) for semiconductor components which have a small size and fine pitch wiring.
One exemplary CSP is shown in FIG. 1. The package 20 has a board-on-chip (BOC) construction whereby a semiconductor component, such as an integrated circuit (IC) chip 202, is attached to a base material, such as a substrate 206, with an adhesive material 204. The adhesive material 204 is interposed between and bonds the IC chip 202 and the substrate 206. The package 20 also includes electrical connectors, e.g. solder balls 208 and metal wires 210, for connection of the IC chip 202 to external components.
Conventional adhesives used in BOC packages are designed to exhibit certain reliability characteristics due to the adverse environments encountered during subsequent manufacturing and assembly processes. For example, adhesives used in BOC packages must be stable at high temperatures (e.g., greater than about 150 degrees Celsius) in order to ensure reliability of the package during subsequent processing such as exposure to a high-temperature solder bath.
In addition, health-related issues present other design factors for conventional adhesives used in BOC packaging. For example, to avoid excessive PCB outgassing, adhesives used in BOC packages must permit attachment at low temperatures (e.g., lower than about 150 degrees Celsius).
A problem exists with conventional adhesives used in BOC packaging in that these materials often represent a compromise between the low temperature attachment and high temperature stability requirements. These adhesives usually comprise a hybrid material or mixture composed of two materials that differ in glass transition temperature (Tg), often combined in an epoxy blend. The glass transition temperature, Tg, is the temperature at which a rigid glass becomes rubbery. A conventional hybrid adhesive may combine a low Tg material, which exhibits the desired low temperature attachment characteristic, with a high Tg material, which exhibits the desired high temperature stability characteristic. The resulting blend usually exhibits attachment and stability characteristics that fall between the two materials, but possess the desired attachment and/or stability qualities of neither material.
Therefore, there is a strong need and desire for an adhesive material for use in semiconductor packages that exhibits the desired attachment characteristics of available low Tg materials and the stability qualities of available high Tg materials.
An apparatus and method for forming a board-on-chip (BOC) package is provided. An adhesive material including a carrier and microcapsules distributed in the carrier is provided which may be used to bond a semiconductor component to a mounting surface in a BOC package. The microcapsules contain a hardener and/or a catalyst that, when combined with the carrier, initiate a bonding reaction. The contents of the microcapsules are released via application of an external influence, such as pressure or heat, when the bonding reaction is desired to begin. The use of microcapsules permits the use of adhesive blends with increased stability and reliability at high temperatures, as well as favorable low temperature reaction and bonding characteristics. In addition, the microencapsulated adhesive blend exhibits substantially increased pot life.
In another aspect of the invention, the use of microcapsules permits formulation of adhesive materials suitable for use in semiconductor packages allowing room-temperature attachment.
The adhesive material may also be formulated in an adhesive tape for ease of use in BOC packaging applications.